Abstract
The effect of hydrogels containing nanosilica (NSi) on the autogenous shrinkage, mechanical strength, and electrical resistivity of cement pastes was studied. The interaction between the hydrogels and the surrounding cementitious matrix was examined using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The addition of hydrogels decreased autogenous shrinkage in the cement pastes and this reduction showed a dependence on the concentration of NSi in the hydrogels. Compressive strength and electrical resistivity were reduced in the cement pastes with hydrogels and this reduction was decreased with increased concentration of NSi in the hydrogel. A change in the phase composition of the cement paste in the region close to the hydrogel was noted, compared to the region away from the hydrogel. In a lime solution with increased pH and temperature, Ca(OH)2 and CaCO3 were found to form within the hydrogels; evidence of calcium-silicate-hydrate (C-S-H) formation in the hydrogels with NSi was obtained, indicating the possible pozzolanic potential of the hydrogels with NSi.
Highlights
NSi demonstrated a lower absorption in distilled water and synthetic pore solution than hydrogels without NSi
A general reduction in compressive strength in the pastes with hydrogels was noticed and this reduction was decreased with an increased concentration of NSi in the hydrogels
All pastes with hydrogels showed a lower electrical resistivity compared to the control cement paste
Summary
A major challenge related to high-performance concrete (HPC) is the durability issues arising from the autogenous shrinkage cracking in this material system [1]. This is caused by a low water-to-cement ratio used in the formulation of HPC [2]. To remedy autogenous shrinkage-induced cracking, and ensuing durability issues, the use of internal curing agents, including saturated lightweight aggregates, superabsorbent hydrogels, expanded clay and pumice, has been attempted in the past [6]. Factors including the mixed design of cementitious materials and the physical and chemical characteristics of hydrogels are key in how hydrogels influence the properties of cementitious materials [7,8,17,18,19]
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